So, from what I know, your eyes simply would not be dilated when you sleep, because they simply do not dilate and you could not see that right? You should know dilated eyes are resulted from some drug use and panick or surprise occasions. Maybe sometimes your eyes would be dilated but that is not a serious problem, they would be normal before long.
When you have the dream in the sleep, your eyeballs are actually moving. You may find that your eyeballs are moving at the intense state although you close your eyes. When your dream is in the intense state, your pupils may be dilated which other people could not notice them. However, it will not last for longer time before it releases itself.
Well, in my opinion, it is not possible to have dilated pupils when you are sleep. According to the experts, there are many different factors which can cause pupils to be dilated such as high blood pressure, anxiety, drug use, illness, and trauma etc. And dilated pupils occur, when the pupils, the black part of the eye are bigger than normal. Also, we can say that dilated pupils look like a big black circle. So you should pay attention to them.